The triplication of the amyloid precursor protein gene, found on chromosome 21, is hypothesized to cause overexpression of amyloid-β which leads to amyloid-β plaques in the brain by the fifth decade of life (Mann et al., 1990; Annus et al., 2016)—an early feature of the neuropathology characteristic of Alzheimer’s disease. This evidence concerns the gene APP and early-onset autosomal dominant Alzheimer disease.